1. Field of the Invention
The invention relates to coatings and sterilization of coatings for devices with a medical use.
2. Description of the Related Art
Many polymeric materials can be used as medical device and implant fabrication materials. To improve the biocompatibility of these materials, surface modifications and coatings are used to reduce thrombosis or rejection. The modification or coating of these materials require several processing steps to accomplish the material coating. Substrates modified by each of these methods also require a sterilization method to finalize the product for use by the manufacturer. This introduces the issue of stability of the modified surface under the sterilization process, as the coating materials may not be compatible with traditional sterilization methods.
Different methods of surface modification have been documented in the literature for the purpose of favorable host-material response. Several U.S. patent documents provide means to coat biomedical devices, particularly those in contact with blood such as stents, but do not address the problem of subsequent sterilization (U.S. Pat. Nos. 4,656,083; 5,034,265; 5,132,108; 5,244,654; and 5,409,696) Palmaz et al, in a review of intravascular stents, is skeptical of the use of stent coatings (Palmaz, J., F. Rivera and C. Encamacion. Intravascular Stents, Adv. Vasc. Surg., 1993, 1:107-135). However, Kocsis et al. report that the use of heparin-coated stents was effective to reduce thrombogenicity of the stent surface (Kocsis, J., G. Llanos and E. Holmer. Heparin-Coated Stents, J. of Long-Term Effects of Medical Implants, 2000, 10 19-45)
Typical modifications include hydrophilic and/or hydrogel coatings such as polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG), or Hyaluronic acid (HA), on the surface of cardiovascular implants (stents and pacemakers) or indwelling medical devices, topical wound healing applications, contact lenses, intraocular lenses, etc. Hydrophobic or lubricious coatings are used for medical devices such as coronary or neurovascular guidewires, sutures, needles, catheters and trocars. Bio-active coatings are used for directed cell response such as cell adhesion molecules (CAM, such as RGD (amino acid sequence Arg-Glu-Asp), laminin, collagen, etc.) in tissue engineering applications or adhesion prevention coatings to be used on medical devices such as vena cava filters or small diameter vascular grafts. Coating material also include infection resistance coatings or antimicrobial containing coating. Some coatings also provide for sustained drug release such as sustained release of drug from stents, or as a hydrophobic overcoat to extend the release time of a drug loaded depot. Bio-active coatings containing therapeutic agents such as heparin, phosphoryl choline (PC), urokinase, etc., are used for antithrombogenic properties.
The coatings can be used to deliver therapeutic and pharmaceutic agents such as, but not limited to: antiproliferative/antimitotic agents including natural products such as vinca alkaloids (i.e. vinblastine, vincristine, and vinorelbine), paclitaxel, epidipodophyllotoxins (i.e. etoposide, teniposide), antibiotics (dactinomycin (actinomycin D) daunorubicin, doxorubicin and idarubicin), anthracyclines, mitoxantrone, bleomycins, plicamycin (mithramycin) and mitomycin, enzymes (L-asparaginase which systemically metabolizes L-asparagine and deprives cells which don""t have the capacity to synthesize their own asparagine; antiproliferative/antimitotic alkylating agents such as nitrogen mustards (mechlorethamine, cyclophosphamide and analogs, melphalan, chlorambucil), ethylenimines and methylmelamines (hexamethylmelamine and thiotepa), alkyl sulfonates-busulfan, nitrosoureas (carmustine (BCNU) and analogs, streptozocin), trazenesxe2x80x94dacarbazinine (DTIC); antiproliferative/antimitotic antimetabolites such as folic acid analogs (methotrexate), pyrimidine analogs (fluorouracil, floxuridine, and cytarabine), purine analogs and related inhibitors (mercaptopurine, thioguanine, pentostatin and 2-chlorodeoxyadenosine {cladribine}); platinum coordination complexes (cisplatin, carboplatin), procarbazine, hydroxyurea, mitotane, aminoglutethimide; hormones (i.e.estrogen); Anticoagulants (heparin, synthetic heparin salts and other inhibitors of thrombin); fibrinolytic agents (such as tissue plasminogen activator, streptokinase and urokinase), aspirin, dipyridamole, ticlopidine, clopidogrel, abciximab; antimigratory; antisecretory (breveldin); anti-inflammatory: such as adrenocortical steroids (cortisol, cortisone, fludrocortisone, prednisone, prednisolone, 6xcex1-methylprednisolone, triamcinolone, betamethasone, and dexamethasone), non-steroidal agents (salicylic acid derivatives i.e. aspirin; para-aminophenol derivatives i.e. acetominophen; Indole and indene acetic acids (indomethacin, sulindac, and etodalac), heteroaryl acetic acids (tolmetin, diclofenac, and ketorolac), arylpropionic acids (ibuprofen and derivatives), anthranilic acids (mefenamic acid, and meclofenamic acid), enolic acids (piroxicam, tenoxicam, phenylbutazone, and oxyphenthatrazone), nabumetone, gold compounds (auranofin, aurothioglucose, gold sodium thiomalate); immunosuppressive: (cyclosporine, tacrolimus (FK-506), sirolimus (rapamycin), azathioprine, mycophenolate mofetil); Angiogenic: vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF); nitric oxide donors; anti-sense oligo nucleotides and combinations thereof.
Coating may be formulated by mixing one or more therapeutic agents with the polymeric coating mixture. The therapeutic agent may be present as a liquid, a finely divided solid, or any other appropriate physical form. Optionally, the coating mixture may include one or more additives, e.g., nontoxic auxiliary substances such as diluents, carriers, excipients, stabilizers or the like. Other suitable additives may be formulated with the polymer and pharmaceutically active agent or compound. For example, hydrophilic polymer may be added to a biocompatible hydrophobic coating to modify the release profile, or a hydrophobic polymer may be added to a hydrophilic coating to modify the release profile. One example would be adding a hydrophilic polymer selected from the group consisting of polyethylene oxide (PO), PVP, PEG, carboxymethyl cellulose, and hydroxymethyl cellulose to a hydrophobic (co)polymer coating to modify the release profile. Appropriate relative amounts can be determined by monitoring the in vitro and/or in vivo release profiles for the therapeutic agents.
Methods for surface modification typically include a surface activation step followed by the coupling of the desired molecule. Surface activation is usually achieved by an energy assisted gas phase reaction (plasma, pulsed plasma, flow discharge reactive chemistry (FDRC), corona discharge, etc.) and/or activating the substrate with a highly reactive leaving group (Nxe2x80x94OH succinimide, imidizole, etc.); Functionalization of the surface with self-assembly molecules (SAM, functional silanes and thiols); Controlled hydrolysis of the esters and amides at the surface (polyethylene terephthalate (PET), polylactic acid (PLA), polyglycolic acid (PGA), etc.). Coupling reactions are typically accomplished by carbodiidimide chemistry, reductive amination, malemide-thiol reactions, etc.
Photochemical surface modifications are usually preferred since this method typically does not require a prior surface activation step. Arylketone based chemistry, azide chemistry, acrylate chemistry are key examples.
Sterilization
Most of the coating methods require several processing steps to accomplish the material coating. Substrates modified by each of these methods also require a sterilization method to finalize the product for use by the manufacturer. This introduces the issue of stability of the modified surface under the sterilization process. Conventional sterilization methods such as steam, radiation, and ethylene oxide negatively impact the activity of the coating. Further, radiation (gamma and e-beam), under the conditions evaluated, were shown to induce no grafting of the active heparin component.
Sterilization methods, such as gamma, e-beam and ethylene oxide have been used to sterilize devices which have been previously coated or surface modified. However, there is a need to do both the grafting coating and sterilization in one process by a mechanism that does not severely impact the activity of the bio-active coating.
The present invention relates to a method of sterilizing a material including the steps of:
1. applying the material with a bioactive coating containing polymerizable chemical;
2. polymerizing the bioactive coating on the material; and
3. sterilizing the material and the bioactive coating with a sterilization process such as hydrogen peroxide employing gas plasma.
In one embodiment of the invention at least a portion of the polymerizing step and the sterilizing step occur simultaneously. In another embodiment of the invention the method includes grafting the bioactive coating on said material. In a preferred embodiment, at least a portion of the polymerizing step, grafting step, and the sterilizing step occur simultaneously.
In one embodiment of the invention the material may include metal, non-metal, polymer or plastic, elastomer, or biologically derived material. In one embodiment, the material is selected from the group including stainless steel, aluminum, nitinol, cobalt chrome, and titanium. In an alternate embodiment, the material is selected from the group including glass, silica, and ceramic.
In another embodiment of the invention the material is selected from the group including polyacetal, polyurethane, polyester, polytetrafluoroethylene, polyethylene, polymethylmethacrylate, polyhydroxyethyl methacrylate, polyvinyl alcohol, polypropylene, polymethylpentene, polyetherketone, polyphenylene oxide, polyvinyl chloride, polycarbonate, polysulfone, acrylonitrile-butadiene-styrene, polyetherimide, polyvinylidene fluoride, and copolymers and combinations thereof.
In another embodiment of the invention the material is selected from the group including polysiloxane, fluorinated polysiloxane, ethylene-propylene rubber, fluoroelastomer and combinations thereof.
In another preferred embodiment, the material is selected from the group including polylactic acid, polyglycolic acid, polycaprolactone, polyparadioxanone, polytrimethylene carbonate and their copolymers, collagen, elastin, chitin, coral, hyaluronic acid, bone and combinations thereof.
In one embodiment of the invention the bioactive coating is selected from the group including biocompatible coating, infection resistance coating, antimicrobial coating, drug release coating, antithrombogenic coating and lubricious coating.
In one preferred embodiment of the invention, the bioactive coating contains heparin, phophoryl choline, urokinase or rapamycin.
The bioactive coating may include a hydrophilic or hydrophobic coating. In a preferred embodiment, the bioactive coating is selected from the group including polyvinyl pyrrolidone, polyethylene glycol, polypropylene glycol, polyethylene glycol-co-propylene glycol, polyethylene glycol acrylate, polyethylene glycol diacrylate, polyethylene glycol methacrylate, polyethylene glycol dimethacrylate, polyethylene oxide, polyvinyl alcohol, polyvinyl alcohol-co-vinylacetate, polyhydroxyethyl methacrylate, and polyhyaluronic acid, and hydrophilically substituted derivatives, monomers, unsaturated pre-polymers, and uncrosslinked polymers with double bonds thereof.
In another preferred embodiment, the bioactive coating is selected from the group including polytetrafluoroethylene, polyethylene, polypropylene, poly(ethylene terephthalate), polyester, polyamides, polyarylates, polycarbonate, polystyrene, polysulfone, polyethers, polyacrylates, polymethacrylates, poly(2-hydroxyethyl methacrylate), polyurethanes, poly(siloxane)s, silicones, poly(vinyl chloride), fluorinated elastomers, synthetic rubbers, poly(phenylene oxide), polyetherketones, acrylonitrile-butadiene-styrene rubbers, poyetherimides, and hydrophobically substituted derivatives thereof and their precursor monomers.
In a preferred embodiment, the disclosed method of sterilizing and polymerizing a bioactive coating on a material includes the steps of:
1. applying the material with a bioactive coating containing non-polymerized but polymerizable chemical; and
2. simultaneously polymerizing the bioactive coating and sterilizing the material and bioactive coating with a sterilization process which includes hydrogen peroxide employing gas plasma.
In a preferred embodiment, the method further includes the step of grafting the bioactive coating on the material. In a more preferred embodiment, at least a portion of the polymerizing step, grafting step, and the sterilizing step occur simultaneously.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.